The Boxer Running Club star finished second in the opening Grand Prix race in Cape Town in March and currently sits second on the overall leaderboard.
Her absence in KwaZulu-Natal is expected to affect her chances of keeping pace in the title race.
Xaba told SABC Sport that she had little choice but to accept the overseas opportunity.
However, she confirmed that she plans to return for the Tshwane leg of the series on 1 August.
"Yes, there is a possibility that I will miss the SPAR Durban because of preparation I am looking forward to. I can confirm that I got an invitation to a race that is around 4 July so to do a Spar Women's race will affect me because I need the fresh legs when it comes to the race that," said Xaba
"I am going to because when they invite you they see the potential in you and I don't think it's a good idea to mess that up if I want to be at the top level. I need to go there with fresh legs so that they will invite me next time."
"It will be hard missing the Spar Durban because I will be left behind with points but I will make sure I will hard when the Spar Tshwane comes and work hard to get the bonus points and also try to win it to catch up with the other athletes who are on the Grand Prix standings."
The defending Cape Town Marathon champion did not disclose the name of the European event, saying the race has not yet been officially announced by her agent and organisers.
She did, however, confirm that she will compete in a 10km race in Europe in July as part of her international campaign.
The 31-year-old athlete, who recently finished third at the Istanbul Half Marathon in Turkey, says competing internationally is helping her grow as an athlete.
Xaba explained that the races are giving her valuable experience, especially when it comes to race strategy and competing against some of the world’s top runners. She also sees the European race as important preparation for the World Half Marathon Championships in September.
Xaba also admitted that she was disappointed after the Absa Run Your City Cape Town 10km race was cancelled because of bad weather.
She believes the race would have played an important role in her preparations for the upcoming European event and helped her maintain momentum ahead of her overseas trip.
Despite the disappointment, Xaba said the cancellation was beyond anyone’s control and she remains focused on continuing her training programme.